Image processing devices that read images of a document operate by irradiating light from a light source such as a fluorescent lamp, etc., onto a document. The document may include, for example, text or image data that has been recorded on a paper surface, and the image processing device may perform different functions such as those of a copier or a scanner. In such devices, light that is reflected from the document is received by a light reception unit where it is imaged by an imaging lens onto a light receiver that is equipped with a photoelectric conversion device, such as a CCD. Generally, the imaging lens and photoelectric conversion device must be in predetermined positions for proper input of the data.
One or more mirrors are generally used to guide light that has been reflected from the document onto the light reception unit. In a still-document-type image reading device, because the light path length from the document to the light reception unit needs to be maintained constant when an illuminated portion of the document changes, a mirror is commonly arranged so that it can be moved along the document.
The structure of this type of image reading device is shown in FIGS. 8 and 9. FIG. 8 is a schematic perspective view showing the structure of a still-document-type image reading device 1. Two guide plates 2b, 2e that resemble shelves are provided on the sidewall of a longitudinal wall 2a of a housing 2 of the image reading device 1. A full-traverse carriage 3 is then loaded onto the guide plates 2b and a half-traverse carriage 4 is then loaded onto the guide plates 2e. These carriages are guided by the guide plates 2b, 2e, respectively, and are moved in the longitudinal direction of the housing 2, which serves as a frame for supporting the components of the image reading device and also to block extraneous light from reaching the light reception unit. A non-illustrated platen, preferably made of glass, is mounted on the top surface of the housing 2, and a document is then loaded on the platen. A light source 5, such as a fluorescent lamp, is loaded on the full-traverse carriage 3, and the document is illuminated by the light source. Furthermore, a light receiver 20 that is equipped with an imaging lens 6 and a photoelectric conversion device 7, such as a CCD etc., is provided at a suitable position on the base plate 2c of the housing.
Then, a first reflecting mirror (not illustrated) is provided on the full-traverse carriage 3 and second and third reflecting mirrors (not illustrated) are provided on the half-traverse carriage 4. A light source 5 illuminates a portion of the document, and light that has been reflected from the document is incident onto the first mirror, the second mirror, and the third mirror, in that order, and is then imaged by the imaging lens 6 onto a surface of a photoelectric conversion device 7. Thus, an optical path is formed from the document to the photoelectric conversion device 7 by the first, second and third mirrors. Since nearly the entire area of the document must be illuminated in order to acquire all the information contained on the document, the till-traverse carriage 3 should be movable over nearly the entire area of the platen glass. However, the length of the optical path from the portion of the document being read at any particular instant to the photoelectric conversion device 7 must also be kept constant. Therefore, the half-traverse carriage 4 is driven to move in synchronism with the full-traverse carriage 3, but at a rate of movement that is half that of the full-traverse carriage.
FIG. 9 is a schematic diagram which illustrates, in perspective view, a driving mechanism for moving the full-traverse carriage 3 and the half-traverse carriage 4. A shaft 8 that is aligned normal to the scanning direction of the carriages is supported so as to rotate near one end of the housing 2, and a pulley 8a is fitted into the central part of the shaft 8. A motor 9 is fixed to the base plate 2c of the housing, and a pulley 9a is fitted onto an output shaft of the motor. A first belt 11a is driven by the motor via the pulley 9a so as to drive a first intermediate pulley 10a and a second intermediate pulley 10b. The pulley 10b is integrally attached to the pulley 10a but has a smaller diameter. A second belt 11b is driven by the second intermediate pulley 10b. In this fashion, the motor 9 causes the shaft 8 to rotate, but at a rate that is slower than the rotation rate of the motor. Due to the reduced rotation rate of the shaft 8 as compared to that of the motor, vibrations of the carriages as they are moved along beneath the platen are reduced. Reduction of vibrations becomes especially important as the size (and hence mass) of the image processing device is reduced.
A drive pulley 13 is fitted onto one end of the shaft 8, and a wire rope 14 is wound several times around the drive pulley 13. A pair of intermediate pulleys 15, 16 are provided which are independently rotatable about a common shaft that is attached to the half-traverse carriage 4, with the axial direction of the shaft that supports these pulleys being aligned with the axial direction of the shaft 8. A pulley 17 is supported so as to be rotatable about a shaft near an opposite end of the housing 2 from the shaft 8, with the axial direction of the shaft which supports the pulley 17 being aligned with the axial direction of the shaft 8. Furthermore, a bracket 2d is provided at a position along a wall 2a of the housing 2, with the drive pulley 13, wire rope 14, pulleys 15, 16, 17, and bracket 2d all being positioned inside the housing 2.
In order to drive the carriages, one end of the wire rope 14 is fixed to the bracket 2d. The wire rope 14 then passes half-way around the pulley 16, and is attached to the full-traverse carriage 3 by a linking part 18. The wire rope 14 then passes several times around the drive pulley 13, passes half-way around the pulley 17 which is fixed in position relative to the housing 2, and then half-way around the pulley 15. The other end of the wire rope 14 then attaches to one end of a spring 19, which may be shaped as a coil. The other end of the spring 19 is attached to a sidewall of the housing 2. The linking part 18 includes a tongue 18a which projects from a base plate that forms the full-traverse carriage 3, and a screw 18b which may be threaded into the linking part 18. The wire rope 14 is clamped by the screw 18b and the tongue 18a so as to attach the wire rope 14 to the full-traverse carriage 3.
As taught in Japanese Laid Open Patent Publication H10-257251, the motor 9 may be attached to the bottom plate 2c of the housing 2 in order to achieve miniaturization of the image processing device. Therefore, vibrations of the motor 9 will inherently be transmitted via the housing 2 to the guide plates 2b and 2e, and this may cause the carriages, which are mounted on the guide plates 2b and 2e, to vibrate.
In recent years, an increase in the speed of image processing devices has come to be desired, and this has resulted in an increase in the moving speeds of the carriages. Even if the vibration of the motor 9 is made to be small, when the carriage speeds are further increased, there is a likelihood that vibrations which will result from the faster carriage movement will cause the obtained image data of the receiver unit to be degraded.